1. Field of the Invention
The present invention relates to a five-speed automatic transmission which is mounted on a front-engine rear-wheel drive vehicle, and a hydraulic control system thereof.
2. Background of the Related Art
As is widely known, an automatic transmission for a vehicle comprises at least two planetary gearsets. Each planetary gearset includes three elements: a sun gear; a ring gear; and a planet pinion gear carrier supporting at least one pinion gear engaged with and arranged between the sun and ring gears. Shifting operations are performed by selecting one of the elements as a reacting element, another as an input element, and another as an output element.
A conventional 4-speed automatic transmission includes a conventional 3-speed automatic transmission assembly having two planetary gearsets, and additionally includes an overdrive assembly or underdrive assembly, which includes an additional planetary gearset.
Japanese laid-open Patent Publication No. S51-48062 discloses a five-forward speed, two-reverse speed automatic transmission which includes, in combination, two sets of single pinion planetary gearsets and a double pinion planetary gearset. In this automatic transmission, however, the operational states of two clutch members and two brake members must be switched when shifting from a second speed to a third speed or vice versa. This causes a shift shock to occur, and the shift control is relatively complicated.
To solve the above described problem, Korean Patent Publication No. 93-10896 discloses a five-speed automatic transmission including three sets of single pinion planetary gearsets, each of which has a sun gear, a ring gear, and a planet pinion carrier supporting a planetary pinion gear engaged with and arranged between the sun and ring gears. In this transmission, the ring gear of the first planetary gearset is permanently connected to the planet carrier of the second planetary gearset, or is selectively connected to the planet carrier of the second planetary gearset through a friction member (i.e., a clutch or a brake). Furthermore, the planet pinion gear carrier of the first planetary gearset is selectively connected to the ring gear of the third planetary gearset through a friction member. The sun gear of the first planetary gearset is permanently connected to the planet pinion gear carrier of the third planetary gearset, or is selectively connected to the same through a friction member.
In this transmission, to alleviate a shift shock, additional elements besides a one-way clutch are used for the friction members, which makes the structure complicated, and increases the overall size. Thus, there is an increase in the manufacturing cost.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.